The present invention relates to applications of a multilayered superconducting material wherein a mercuric halide-organic complex is intercalated between the unit lattices of a Bi-based high-temperature superconductor. More specifically, the present invention relates to superconducting colloids produced by exfoliating the multilayered material, produced by intercalating mercuric halide between the layers of raw material, Bi-based high-temperature superconductor, and reacting said mercuric halide with a chain-like organic halide salt between layers, wherein oxide superconducting layers and organic layers alternately repeated in said multilayered material. The present invention also relates to a superconducting thin layer produced by using said colloid as a precursor and the process thereof.
Sputtering, molecular beam epitaxy (MBE), laser ablation, chemical vapor deposition (CVD), etc. have hitherto been used as the technology for manufacturing superconducting thin layers. However, these technologies demand more complex techniques (high temperature, ultra-vacuum, etc.) and high costs. In addition, the processing time becomes very long when forming films of a micrometer in thickness. These technologies also have drawbacks in that they cannot easily be used to obtain films having a large surface area, and these techniques require a planar substrate. Further, a thin layer can be made by depositing a sol-gel and heat-treating it. In such instances, however, the quality of the thin layer deteriorates because the organic material is burned and escapes in the form of gas, and voids are formed on the surface thereby making the surface uneven. In the conventional manufacturing process of layers using electro-deposition, a layer is produced by grinding a superconductor or by electro-depositing a precursor solution. In the former, however, a thin layer cannot be produced because the particles are a micrometer in size, and, in the latter, the superconducting properties are formed only after heat-treatment at high temperatures.
Therefore, there has been a need in the art for an economical, convenient and rapid process for producing a superconducting thin layer.
A Bi-based superconductor is an oxide comprising Bi, Sr, Ca, Cu, etc., and can be represented by the formula shown below depending on the composition ratio and the number of copper-oxygen planes (m) included in a unit lattice:
Bi2Sr2Camxe2x88x921CumO2m+4+xcex4
wherein m is 1, 2 or 3 and represents the number of copper-oxygen planes included in a unit lattice and 2m+4+xcex4 is the content of oxygen; wherein xcex4 is a positive number greater than 0 and less than 1 and varies depending on synthesis conditions, such as the partial pressure of oxygen. In addition, each metal atom may be substituted with a different metal ion having a similar ionic radius. Accordingly, Bi may be substituted with Pb; Sr may be substituted with any one of La, Pr, Nd or Ca; Ca may be substituted with Y; and Cu may be substituted with any one of Co or Fe.
Because a Bi-based superconductor commonly has a weakly bonded Bixe2x80x94O double layer, different chemical species may be intercalated between the double layer without causing a change in the metal oxide lattice. The Bi-based superconductor having iodine [Nature, 348, pp.145-147] or mercuric halide [J. Am. Chem. Soc. 116, 1994, pp. 11564-11565] intercalated therein is known as a superconducting intercalate. In this instance, however, the distance between layers cannot be readily controlled because the intercalates are all inorganic atoms or molecules.
In order to solve these problems, the inventors of the present invention previously synthesized a layered-structure superconductor, wherein a mercuric halide-organic material complex is intercalated between layers. The synthesis was carried out by reacting mercuric halide intercalated in a Bi-based superconductor with organic (cation)-halogen (anion) salt (Korean Patent Application No. 1997-50741; and Science, 280, 1998, pp.1589-1592). Using this procedure, it was readily possible to control the distance between the superconductor layers by intercalating an organic material having a saturated alkyl chain into the layered-structure Bi-based superconductor.
Before the present invention, however, there had not been any examples in which the superconducting material as disclosed in the above Korean patent application (wherein a mercuric halide-organic material is intercalated) is used in the preparation of a superconducting thin layer.
Since filing of the above Korean patent application, the inventors have continued to conduct research in this field, and have found that when the organic chain intercalated into a Bi-based high temperature superconductor is long, i.e., the number of carbon atoms is large, the distance between the layers becomes so great that the bond strength between the lattices of oxide superconductor can be disregarded. If the superconductor is washed with an aprotic organic solvent treated with supersonic waves, the mercuric halide-organic material complex intercalated between the layers is dissolved in the solvent, and the lattices of the superconductor can be exfoliated into each layer.
Further, the inventors have found that the aforesaid exfoliation procedure can be used to produce superconducting colloid particles having a molecular level thickness, and that a superconducting thin layer can be produced in an economical way by using these superconducting colloid particles as precursors in the production of superconducting thin layers.
Accordingly, a purpose of the present invention is to provide a superconducting colloid that can be used as a precursor in the production of a superconducting thin layer. The superconducting colloid can be produced by using a Bi-based superconductor having an organic material intercalated therein, and the superconducting thin layer can be produced in an economical way by using the colloid as a precursor.
Another purpose of the present invention is to provide a process for producing the superconducting colloid of the invention.
Another purpose of the present invention is to provide a superconducting thin layer produced by using the superconducting colloid of the invention and the process for production thereof. The production of superconducting thin layers using the superconducting colloid according to the present invention and the electro-deposition method can be applied to a superconducting thin layer having a large area that cannot be produced in an established method or using a substrate with a three-dimensional shape, such as a curvature, a cylinder and the like. The process for forming superconducting thin layers of the invention can also be used in a variety of applications, such as magnetocardiography, where a magnetic field shielding is required, and electronics wherein a superconducting thin layer is used.